1. Field of the Invention
This invention relates generally to pneumatic trailers, and more particularly to a pneumatic drop frame trailer having a pneumatic suspension system that moves the trailer chassis between a lowered loading and unloading position disposed horizontally on a support surface and a raised towing and load-carrying position supported by pressurized air bladders.
2. Brief Description of the Prior Art
Trailers for towing such items as motorcycles behind a car, truck or recreational vehicle are well known. The common trailer design consists of a solid axle to which wheels are mounted on opposite ends of the axle. Springs are attached to the axle at the widest location. The forward spring attachment is rigidly secured to an outside frame member for fore-to-aft axle stability and is attached to a rigid frame mount by a flexible spring hanger at the rearward end of the frame member. Typically, two longitudinal frame members are joined by load-carrying, transverse frame members upon which the trailer deck is mounted. The deck, by necessity, is located above the axle the distance of the upward wheel travel plus the thickness of the deck and deck frame. It is not uncommon for trailers to have a deck positioned 6″ or so above the center of the axle. When loading heavy items onto the trailer, it is common to utilize a ramp at the back end of the trailer or to tilt the trailer about the wheel axle to engage the ground and then move the items up the inclined ram or deck.
Trailers having pneumatic shock absorbers, air cylinders, or air bladders that perform a dual function of absorbing road shocks and of raising and lowering the trailer bed are also known in the art.
Smith, U.S. Pat. No. 6,382,647 discloses a trailer apparatus having pneumatic shock absorbers that perform a dual function of absorbing road shocks and of raising and lowering the trailer bed. The trailer apparatus also includes king pin elements which move between positive and negative caster to provide stability and ease of backing the trailer.
Kallstrom, U.S. Pat. No. 6,349,952 discloses a trailer with a frame having a center load receiving channel for a motorcycle or for a similar load with a pair of opposed laterally extending wheel axles pivotally mounted at their inward end near the center channel. Bladder type air cylinders extend between the frame and axles near the outer end of the axles. An air suspension system controls the inflation of the air cylinders during transit and allows the trailer to be lowered to a position close to the ground. The air cylinders are mounted inboard of the wheel assemblies and, thus, the wheels pivot upwardly and angularly inward from each side with respect to the longitudinal axis of the frame when the frame is lowered.
Evans, U.S. Pat. No. 2,957,593 discloses a boat trailer having air bags or casings for lowering one end of the trailer and connected by linkages with boat supporting rollers that are automatically raised when the end of the trailer is lowered to facilitate loading and unloading of a boat thereon.
The present invention is distinguished over the prior art in general, and these patents in particular by a pneumatic drop frame trailer having lateral wheels connected by a pivotal wheel support arm to the frame with airbags connected between the support arm and the frame, a pivotal tongue member with an airbag connected between the tongue and the frame, and a deck having an inclined ramp portion at the rear end. The wheel airbags may be inflated or deflated to selectively raise and lower the frame relative to the ground, and may also be inflated to provide the desired stiffness or shock absorbing characteristics for absorbing road shocks as the trailer is towed. The tongue airbag may be inflated or deflated to allow the frame and deck to be selectively raised and lowered with respect to the tongue and/or the towing vehicle. When the wheel airbags are deflated, the bottom of the frame is disposed substantially horizontally and supported on the ground surface in a loading and unloading position. When the trailer is hitched to a tow vehicle, the load supporting deck can be lowered evenly and horizontally positioned very close to the ground, and the rearward end of the ramp portion of the deck is substantially flush with the ground surface to facilitate moving items onto the deck. A control box disposed on the deck contains an air compressor, an air storage tank, and associated control elements including appropriate valves for inflating and deflating the airbags.